We ended up with the following list of language pack files, these files were placed in the WEB-INF\lib folder.
org.eclipse.birt.report.viewer.nl_de_3.5.0.v20110723105825.jar
org.eclipse.birt.report.viewer.nl_es_3.5.0.v20110723105825.jar
org.eclipse.birt.report.viewer.nl_fr_3.5.0.v20110723105825.jar
org.eclipse.birt.report.viewer.nl_it_3.5.0.v20110723105825.jar
org.eclipse.birt.report.viewer.nl_ja_3.5.0.v20110723105825.jar
org.eclipse.birt.report.viewer.nl_ko_3.5.0.v20110723105825.jar
org.eclipse.birt.report.viewer.nl_pt_3.5.0.v20110723105825.jar
org.eclipse.birt.report.viewer.nl_pt_BR_3.5.0.v20110723105825.jar
org.eclipse.birt.report.viewer.nl_zh_3.5.0.v20110723105825.jar
org.eclipse.birt.report.viewer.nl_zh_TW_3.5.0.v20110723105825.jar